5 research outputs found
Tools and Algorithms for the Construction and Analysis of Systems
This open access book constitutes the proceedings of the 28th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2022, which was held during April 2-7, 2022, in Munich, Germany, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2022. The 46 full papers and 4 short papers presented in this volume were carefully reviewed and selected from 159 submissions. The proceedings also contain 16 tool papers of the affiliated competition SV-Comp and 1 paper consisting of the competition report. TACAS is a forum for researchers, developers, and users interested in rigorously based tools and algorithms for the construction and analysis of systems. The conference aims to bridge the gaps between different communities with this common interest and to support them in their quest to improve the utility, reliability, exibility, and efficiency of tools and algorithms for building computer-controlled systems
Bedload transport of sand-gravel mixtures with antidunes: flume experiments
In this thesis, the interaction between flow and sediment in alluvial channels is studied from an empirical approach, for conditions close or pertaining to supercritical flow, and for four types of sediment: sand, gravel and two mixtures with sand and gravel in a relative proportion of 70-30 and 55-45, respectively. The objective is to obtain by means of laboratory experiments a data set with the characteristics of flow, sediment transport, bed configurations and sediment sorting patterns in sediment mixtures, for different conditions within upper- and transitional-regimes. From a practical perspective, the aim of this work is to reproduce similar conditions to those likely to occur in torrential ephemeral streams, common in the Mediterranean coast and known in Spain as ¿ramblas¿.
The experimental work consisted in searching for mobile-bed equilibrium states, for different water discharges and sediment-feed rates. The definitive data set comprises 22 runs, with durations up to 12 hours. Sediment-feed rates were constant during each run, and they were even higher than 1 kg/s. Dominant bed configurations included transitional bedforms and trains of antidunes, coexisting with alternate bars. Antidunes were mostly three-dimensional rather than two-dimensional, and in contrast to the most referred antidunes in literature, the antidunes herein reported moved in the downstream direction and were stable most of the time. Short-crested stationary waves on the water surface accompanied the antidunes.
Characterization of the experimental bedforms allowed identifying the range of Froude numbers in which transitional regime prevails for the studied sediment; also, this characterization allowed assessing the performance of theoretical and empirical diagrams for bedform stability phases. It is here demonstrated that for very coarse sand, fine gravel and mixtures of these two materials, plane bed does not occur in the transition from lower- to upper-regime, and if it would occur, it would be restricted to a very narrow range of Froude numbers. Regarding flow resistance related to bedforms in upper-regime, it has been here probed that for similar geometrical conditions, downstream-migrating antidunes produce less flow resistance than dunes, and more flow resistance than upstream-migrating antidunes.
An important concern in this work has been to investigate the effect of the relative sand content of sediment in bedforms, flow resistance and sediment transport. It is here demonstrated that bedforms in sand beds can be higher and they can produce much more drag than bedforms in gravel and sand-gravel mixtures. Regarding sediment transport, it is here shown that for the high sediment-feed rates tested in the experiments, certain ranges of sand content would affect sediment mobility. Besides sand content, it is shown that the ratio between sand and gravel grain sizes would also be relevant in the mobility of sediment in comparison to well-sorted material. A conceptual model is suggested for computation of sediment incipient motion, which model is based on the variation of bed porosity with sand content and on the relative size between particles.
Some supplementary themes considered in this work include the study of the required conditions for the formation of three-dimensional stationary waves over antidunes; the hydraulic analysis of flow over antidunes and the morphological consequences of such a flow for the three likely regimes of antidune direction of movement; sediment sorting patterns according to sand content, especially bed surface patches of homogeneous sediment; and finally, the analysis of the process by which fine sediment penetrates into a bed composed of particles of diverse sizes.En esta tesis se estudia de manera empÃrica la interacción entre el flujo y el sedimento en
canales aluviales, para condiciones cercanas o pertenecientes al régimen rápido y para
cuatro tipos de sedimento: arena, grava y dos mezclas con grava y arena, en una proporción
relativa de 70-30 y 55-45, respectivamente. El objetivo es obtener de manera experimental
en laboratorio un grupo de datos sobre las caracterÃsticas del flujo, transporte de
sedimento, configuraciones de fondo y patrones de clasificación en mezclas de sedimento,
para diferentes condiciones dentro de los regÃmenes superior y de transición. De manera
práctica, la intención de este trabajo es reproducir condiciones comparables a las que
pueden ocurrir en rÃos efÃmeros de carácter torrencial, comunes en la costa Mediterránea y
conocidos en España como ramblas.
El trabajo experimental consistió en la búsqueda de condiciones de equilibrio
dinámico en lecho móvil, para diferentes caudales lÃquidos y tasas de alimentación de
sedimento. 22 ensayos, con duraciones de hasta 12 horas, conformaron el grupo de datos
definitivo. Las tasas de alimentación fueron constantes durante cada ensayo, y alcanzaron
valores de incluso más de 1 kg/s. Las configuraciones de fondo dominantes incluyeron
formas de fondo de transición y trenes de antidunas, en coexistencia con barras alternadas.
Predominaron las antidunas tridimensionales sobre las bidimensionales y, a diferencia de las
antidunas más referidas en la literatura, las aquà descritas migraban hacia aguas abajo y eran
bastante estables. En la superficie del agua acompañaban a las antidunas ondas
estacionarias de cresta corta.
La caracterización de las formas de fondo experimentales permitió identificar el
intervalo de números de Froude en el cual prevalece el régimen de transición en el
sedimento estudiado y también evaluar diagramas teóricos y empÃricos para las regiones de
estabilidad de formas de fondo. Se demuestra que en arena muy gruesa, grava fina y
mezclas de estos dos materiales, en la transición de régimen inferior a superior no ocurre el
fondo plano, y si asà fuese, estarÃa restringido a un intervalo muy estrecho de números de
Froude. En cuanto a la resistencia al flujo producida por las formas de fondo en régimen
superior, se ha probado que para condiciones geométricas similares las antidunas que
migran hacia aguas abajo producen menos resistencia al flujo que las dunas y más
resistencia que las antidunas que migran hacia aguas arriba.
De particular interés ha sido reconocer el efecto en las formas de fondo, la
resistencia al flujo y el transporte de sedimento, del contenido relativo de arena en el
sedimento. Se muestra que las formas de fondo desarrolladas en lechos compuestos sólo de
arena pueden ser de mayor magnitud y producir mucha mayor resistencia de forma que las
formas de fondo en grava y mezclas de grava-arena. En cuanto al transporte de sedimento,
se muestra que para las altas tasas de transporte probadas ciertos intervalos de contenido de
arena afectan la movilidad del sedimento. Además de la proporción de arena en la mezcla,
el grado de afectación en la movilidad estarÃa relacionado con la relación entre tamaños de
la arena y la grava. Se propone un modelo conceptual para el cálculo del inicio de
movimiento de las partÃculas del fondo, el cual considera la variación de la porosidad en el
lecho con el contenido de arena y la relación de tamaños de las partÃculas.Postprint (published version
GVSU Press Releases, 1971
A compilation of press releases for the year 1971 submitted by University Communications (formerly News & Information Services) to news agencies concerning the people, places, and events related to Grand Valley State University